Technical Field
The present disclosure is directed to dynamically reconfigurable aerial vehicles and, more particularly, to aircraft having multiple thrust generators that can be repositioned relative to one another while in flight or on the ground and a related control system that maintains in-flight stability during repositioning of the thrust generators.
Description of the Related Art
One form of aircraft that utilizes multiple thrust generators is the multicopter. This type of craft utilizes multiple rotors oriented to have a downward thrust. Typically, these rotors are mounted to a fixed frame, usually multiple arms extending outward from a central hub. Because these craft have inherent dynamic instability, sophisticated control systems are used to vary the amount of thrust produced by each rotor to enable controlled ascent, descent, hovering and directional control.
Referring to FIG. 1, shown therein is a multicopter 20 having four rotors 22 mounted on respective arms 24 that extend from a central hub 26, usually in a symmetric manner. Each arm 24 holds a respective rotor 22 at a terminal end 28. A multicopter can have any number of arms, but the most common type of multicopter is a quadcopter, which has the four arms 24 shown in FIG. 1. A common variation is the tricopter, which has three arms, hexacopter, which has six arms, and the octocopter 30, which has eight arms 32, as shown in FIG. 2.
A quadcopter can be of two types depending how the direction of motion is defined by its controller electronics. There is the “Plus” (+) type where the direction of forward motion is along one of the arms, as shown by the denoted F1 in FIG. 1, and there is the “x” type, where the direction of forward motion is along the middle of two adjacent arms, denoted by F2 in FIG. 1.
Flight control is maintained by an on-board receiver coupled to a control system that combines data from small on-board MEMs gyroscopes, accelerometers (the same as those found in smart phones) and signals received at the on-board receiver from a remote transmitter.
Generally, the rotor spins in an opposite direction from the two rotors on either side of it (i.e. in a quadcopter the rotors on opposite corners of the frame spin in the same direction). A multicopter controls roll and pitch by speeding up the rotors on one side of the craft while slowing down the opposing other rotors. If the user wanted the craft to roll left, the user would input signals that would cause the rotors on the right side of the frame to speed up and the rotors on the left slide to slow down. Similarly if the user intended to move the craft forward, the user would cause the back rotors to speed up and the front rotors to slow down.
The craft turns clockwise or counterclockwise (“yaws” as viewed from the top) by speeding up the set of rotors that spin counterclockwise (or clockwise), and slowing down the other set of rotors that spin clockwise (or counterclockwise). Horizontal motion is accomplished by temporarily speeding up or slowing down some rotors so that the vehicle rolls into the desired direction of travel and increasing the overall thrust of all rotors so the overall thrust vector causes the craft to move in the intended direction. Altitude is controlled by speeding up or slowing down all rotors at the same time.
One drawback to current designs is the difficulty or near impossibility of accommodating for an engine-out situation or for a change in the amount or shift in the location of a load carried by the aircraft. In addition, when the craft is flying within a narrow airspace, whether intentionally or inadvertently, there is the high risk of rotor strike with a ground-based object, such as trees, buildings, and other structures. Hence, there is a need for a multicopter design that facilitates continued stable flight in response to changes in the moment of inertia, center of gravity, and center of mass, such as engine failure or when there is a change in the load. There is also a need for an aircraft that can reconfigure itself while in flight to accommodate clearance with ground-based features.